Cam-controlled thread gauge



Mil#

J. HARTNEss CAM coNTRoLLED THREAD GAUGE Sept. s, 1931. 1,822,027

" i "Fied March 2. 1929 1. @iff Patented Sept. 8', QS

UNITED STATES JAMES HARTNESS, OF SPRINGFIELD, VERMONT CAM-CONTROLLED THREAD GAUGE Application mea March 2, 1929. seran No. 343,990.

This invention relates to a gauge for testmovement of the gaging members when the ing screw threads for error in pitch diameter and lead. A gauge embodying the present invention may comprise essentially two threaded members for engagement with a screw thread to be tested, the threaded gauge members being capable of relative rotational gaging motion, the angles of such rotation when the members are' in engage- 10 ment with a master thread being compared with the angles of rotation permissible when the members are in engagement with a screw to be tested. The embodiments of the present invention hereinafter described consist of a pair of ring-shaped members, each having an interior thread to receive an exteriorly threaded screw to be tested. lf either of these gauge members be rotated while `held against axial movement, the gaging thread V will have an apparent axial movement, the

direction depending on the direction ofrotation and on whether it is a right hand or a left hand thread. This apparent axial progress of the thread due to rotation of a member may be modified by bodily axial movement of the member so as to increase, diminish or reverse the apparent motion of the thread. If two such gauge members are held against axial movement and are rotated relatively to each other, their respective threads will have an apparent travel axially in opposite directions. This relative apparent travel of the threads of the gaging members may be modified by controlled relative axial movement of the members as they rotate. W'hen the gaging` members are in engagementwith a screw and their bodily movmcnt is controlled, the mutual approaching and separating motions of the gaging threads cause these threads to bring up against the opposite flanks of the threadsof the screw and thus limit the extents of relative rotation of 'the two'members. The relative bodily movement of the members may, for example, be controlled by mutual threaded engagement, as shown and described in my co-pending application Serial No. 192,- 236, filed May 18, 1927. It the connecting thread hasv a pitch equal to that of the gaging thread there will be no relative apparent members are rotated, as the bodily axial movement of the members will exactly offset Vthe apparent relative movement of the gaging threads. lf the pitch of the connecting thread is less or greater than the pitch of the gaging thread, there will be apparent relative movement of the gaging threads, the rate of such movement per turn of the members depending on the 'difference in pitch between the gaging thread and the connecting thread. Thus, if this diiference is considerable the slack between the gaging threads and the threadof a screw on which the gauge members are mounted is quickly taken up when the members are rotated, whereas if the"v difference is small, considerable relative rotation of the members is necessary to take up the sameamount of slack or looseness. Since the amount of such slack to be taken up is, in the absence of lead error and malformation of the thread, a measure of the flank thickness of the screw to be tested, the relative rotation of the gauge members when in engagement with `the screw is also a measure of the flank thickness. The sensitivity of the gauge may thus be determined by the choice of a connecting thread which diifers in pitch from the gaging thread by little or much according as greater or less sensitivity is desired.

According to the present invention, the gauge members may be connected in such a way that the difference between their relative axial motion and the apparent relative motion of their threads need not be constant, but can be varied as by the use of cams. Thus for example a gauge of this type may be screwed on to a screw threaded member to be tested, then the two gauge members relatively rotated. According to the present invention, the axial movement of the members during such relative rotation may be so controlled that at first there is a quick take-up of most of the slack or loosey ness between the threads of the gauge members and the thread of"the screw, then the rate of take-up may be much slower so thatv thegauge may be'made very sensitive.V

through the zones of tolerance without requirine excessive rotation of the gauge members from the open position to the zones.

For a complete disclosure of the invention, reference is had to the description thereof which follows, and to the drawings, of which,-

Figure l is a front elevation of a gauge of the ringy type embodying theinvention-n Figure 2 is an edge elevation ofthe same.

Figure 3 is a perspective view of'one of" the gaging members of-ithefgaugeillustrated.' in Figure l.

Figure 4 is a perspective vie-:wof a-second gaging member of the gauge shown in Figure l.

FiguieY is aplane cleveloprrnentrof the cam slots in the-peripherali portion of the gaging member illustratedfin Figure 3.

Figure @shows cam slots similar to .those in Figure 5b`utofmodified configuration..

Figure Tis a ,front elemtionV of 'a modified forni of'gauge embodying theinvention.

Figurev 8 is a section-Von the line 8`81 of F igure 7l Figure 9 -is a front' elevationof another modified 'form ofthe invention.

Figure l0-is a'section-on theline l010,l

Figure ll'is an edge elevation of`one. of: the gagingmembers of Vthegaugeshown. in. Figure 9.

Figure 12 is a plane development'offthe eripheral portion of "the -member Y shown ,inl *igure l1;

Figure 13 showsvin elevation a gauge-of` the plug` type embodying the presentinvention.

Figurellis a section on theline lef-let Figure l5 'is an end elevation of fthe Gauge b e v M sho-wn 1n Figure 513.

A' gauge embodying the invention-may have a form somewhat similar to that illusf trated in Figures l'to el; As shownfthis: comprises a pair of'gaging members lin the form of 'perforated'disks One of these; disks 20 is provided with' an axial flange 2l which forms therewith'a recess adaptedto.

receive the other disk 22.' The disk 22i'isv preferably fitted within the flange 21'so as to rotate freely therein. The dis'k 20r`is een trally apertured asat 23 'and the disk' 22`is similarly apertured as at 24, theseapertures being internally threaded for loose fitting engagement )with the largest tolerable thread to be gaged 'when the gauge is-in its open" position, that is.when the gagingthreadslie in a commonV helix. Each thread iis pref-f erably transversely slotted-as at 25 so thatv any dust or other foreign matter which may happen to be on. the flanks `.ofthe thread 'to' be tested will be cleaned 'off as the screw to be tested is screwed into the apertures 23 and .24, such dust vbeing collected vinthe slotsV 25. In order to controlthe relative axial;

bodily movement of the disks 20 and 22, I may form a plurality of slots 26 extending through the flange 2l. The walls of these slots are adapted to act as cam surfaces to guide a corresponding number of pins 27, .(0 or equivalent cam followers, which may be secured ,tothe peripheryhvof the disk 22. The pins ,2:7 besides` acting as: cam ifo'llowers are also convenient handles for operating the gauge. Inaassemblingfaigauge such as that illustrated in Figure l, thedisk 22 may be insertedinto^therecess surrounded by the flange 2l, the pins 27 being thereafter insertedthrough their respective slots 26 and 80 secured. invv radial holes previously. formed in the. edge of-the dsk.22. The pins 27 may. be either screw thIreadedinto. the holes or. driven thereinto `so as to: be securely held.y The -threadslwithinthe apertures 23 and.2iJcf 85` are, preferably somewhatshort, as indica-ted` in1 Figure 2, a portion of the aperture 24 bef ingrbored-,outso as toshorten the threaded. portion thereof. Inthis way thethreadedy engagement offthe gaginginembers 20. and 9o. 22 ona screwto. be tested is at spaced points.A The extentof engagement` of each gagingf membeix is preferably. equivalent to one or two .turns of thread. The distance between thepoints of-engagement of themembers 2O 95p and .22 with ,the thread .to be tested maybe. regulatedzby the. thickness oflthe disk 22, the flange 21 being,preferably.elongated` correspondingly.4 It is preferred to regulate.

the-#distance between the mutually remote.

of an inch, itis preferred to construct thel gauge so that the distance `of-overall engagementofthe gauge with th'escrew to be test 11eedwillhe,approximately an inch.. This fea-. tureis. of Vspecial importance where a lead error'is 'liable to be present-in the screw-to be tested. A". lead-` error which would be. serious in thecaseof athreaded engagement. oflan inch orso.' might notvbe objectionable. ina-:screw ofthesamesiZe if the working threaded engagement thereoffwere to be con'- siderablyV less than an inch..

Thegaging action of thegaging. lmembers 12o arises fromth'efapparent frelativeaxial travel of theinternal'threads ofthe members when the members areA relatively rotated. This approachingor separating movement of the threads takes up the slackof the loose litbetween the gagin-gmembers and the screw to be tested,.the amount .of such slack being indicated byV theL amount v of relative rotation t ofthe members. If, however, thetwo members are fr'ee totravel bodilytoward Voraway. 13G.,`

from each other, such bodily motion may entirely offset the apparent approaching and separating motion of their threads so that the slack between the threads of the gauge members and the thread of the screw to be tested is not taken up at all. By so controlling the relative bodily movement of the gaging members along the axis, the apparent approaching and separating movement ,of their threads can be regulated so as to be relatively large or small for any given angle of relative rotation of the members. The slots 26 may thus each be cut on a helix, the pitch of the helix being different from the pitch of the internal threads oi the member. Iffthe helix of the slots is in the same direction as the helix of the threads the apparent approaching and separating movement of the threads when the members are relatively rotated will be decreased, thus increasing 'the sensitivity of the gauge. By making the slots 26 with a pitch nearly equal to that of the threads oi the members, the gauge may be constructed with as high a degree of sensitivity as desired. For practical purposes, however, it is not desirable ordinarily to have a gauge so sensitive that an unduly large angle ot relative rotation of the members is required to take up the slack between the threads of the gauge and a screw of correct flank thickness. In order to take up. quickly the larger part of the slack and then to have the gauge more sensitive in taking up the remainder of the slack, cam slots 28, such for example as are illustrated in Figure 6, may be provided. These slots. as shown, comprise a central portion which may be in a plane perpendicular to the axis of the gauge. Vhile the pins 27 ride in this portion of the slots, the disks 20 and 22 are heldagainst any relative axial bodily movement so that upon relative rotation the slack between the gauge threads and those of the screw to be tested is taken up comparatively rapidly. The remainder of the slack take-up is more gradual owing to the helical shape of the end portions of each of the slots 28, there being a bodily relative advance between the gaging members when the pins 27 enter the end portions of the slots 28. If desired, the central portion of the slots 28 may be pitched slightly in the direction opposite to the pitch of the end portions, this resulting in a still more rapid initial take-up of the slack between the threads. By varying the conguration of the slots 28, different types of relative advancing and separating motions between the threads of the gaging members may be obtained.

In order to facilitate the observation oi slackness between the threads of the gaging members and the screw to be tested, I may provide an index 29 on one of the gaging members 'to cooperate with suitable scale marks on the other gaging member. As shown, the index 29 is located on the outer face of the disk 22, this index cooperating with suitable markings on the rim of the flange 21. One such mark may indicate the open position for the index 29 when the i Igauge members 22 are in such a position that their interior threads lie in a common helix. Thus when the index 29 is opposite the open mark, the gauge is ready to receivea screw to be tested. It is preferable that when the gauge is in this position the pins 27 are approximately at the mid points of the slots 26.

The employment of gaging members having threads which engage a screw to be tested over relatively short lengths of thread and at axially spaced points assists the operator in distinguishing error of lead from error of flank thickness. Lead error in a screw thread amounts to a virtual crowding together or axial stretching out of the turns of the thread. The most conspicuous result of lead error on a gauge of the type illustrated is an inequality ofreadings as the gaging members are relatively rotated first in one direction and then in the other. If the gaging threads are so made as to-engage the thread under test over short lengths oi' thread and at spaced points, the spacing between the points of engagement magniiies any lead error present by the number of thread turns between the points of engagement. By reason of the short lengths of engagement, the shortening of the angle of throw of the gauge in one direction is approximately balanced by the increase of the angle of throw oi' the members in the opposite direction from the open position. Thus the mean of the two angles of throw will give approximately the angle to which the members would turn if the screw under test had no lead error. Hence this mean angle is an approximate measure ofV the flank thickness oi the thread. While it may usually not be desired to ascertain' the lili amount of lead error of a screw in terms ot any particular unit, it is important to know whether the lead error is sui'licient, in com# bination with whatever error of pitch diameter there may be present, to render the screw unfit for the service for which it is intended. `For this purpose I may indicate Zones of tolerance on the gauge, within which Zones the index 29 must fall if the screw under test is to be accepted. Thus if the pitch diameter is correct or nearly so,

a certain amount of leeway remains for lead error. Conversely, if there is little or no lead error present, the pitch diameter may renderv the screwdeli'cient. All such delicienciesare detachable: by the gauge herein describedsothatino unfit'screw escapes rejection if*` the r gauge is properly 1nanipu. lated.

In order tti-determine the extents -of`rela1 tive' rotation the gaging members should have when'inr Contact with a perfect thread:` gauge may be' to. be: tested, a: master plug screwed into the gauge andthe gaging members relatively rotated in both directions as farzas-they will go until the slack between the threads istaken up each time. Suitable Zero marks may "be made on the rim of the flange'Ql opposite the index 29 when the gangefmembers have been krotated in oppositezdirectionsfse asto take up the slack between" their. threads-and the thread of a standard plugigaugef. .Vhen a screw thread is subsequently testedin the gauge, the anguiar .distance .of the index 29 from the nearest Zero mark'is an' indication of how fa' fromstandard is the flank thickness of the screw under test, in the absence of lead error.` Zones oftolerance mav be indicated on the rimof theflange 2l or. other suitable location, these zonesbeing on either side of the open mark. The markings for suoli Zonesfof tolerance depend upon the `class of lit-desired aswell as the characteristics of structure vof theI gauge itself. These tolerance limits may be found by calculation or they` may be located empirically by the use of master threads which have been accuratelylground to dimensions on the border lines of tolerance.

In placeA of or in'addition vto the teler-` ance VZones indicated on the gauge, there may be-.scale markings to indicate the flank thickness of the thread tested, either in fractions of some unit as an inch or in percentagesof'ther standard flank thicknesses which a 'perfect-screw of the type measured should have. If there `is no lead error present, a scale calibrated in terms of percentage of standard liank thickness will give at once an'A accurate idea as to actual holding strength ofthe screw compared/to that of a perfect screw, since the holding strength is closely related to the flank thickness thereofwhere the contour of the thread is fairly regular' and the lead error is negligible. This `information' isof particular importance where the screw is destined for a use in=1 whichthere is relatively little margin between its maximum holding strength and the actual stresses which .are it; Thus, for: example, in the construction of airv craft, it is desirable to use screwthreaded members of'minimum .weight consistent with required holding power so that itis-.essential to determine how close each threaded .element comes to the holding power`of-aperfectelement ofthe same type.y

A .modified form -of` gauge is illustrated-^ forming f the camV placed upon inFigures7 l and 8; In this -form aidiskiO' is nested'in avrecessformed by an' axial; flange 3l ofva seconddiskl32.'` Insteadofi surfaces in .theffl'ange 31, A howevenlthey are formed by slots 33'1cutf into the periphery of 'therdisk-'Sf Suitable pins 3-l maybeprojected Lth-r'oughthe `rini- 31 to enter. the respectivefslots.33-a1idto act as cani followers=againstithesidesoff the cam slots.- Thefaction :of the -ga-ugefmay-Av be determined as in the 1)1'evious1`carse'b y= suitably shaping'th'eslots33'." The Operai tionof this gauge isidenticalwith that of the gauge showny iii-1F igure l.l

Figure 9 shows affurthermodified form` of the invention, this gauge operatingon 'the saine principleas the ones hereinbefore described. This gauge may"compriseal disk 35 whichcooperates Withfa second'disl'.; Ther latterI is provided with an axial iangev which has an intufrned YlipBS.- Through this inturned 'lip a number offsetfsc-rews39 are passed, the' inner ends ofthesesetscrews being adapted to engage-respectivelycamsurfaces on the sides ofa flanges()A which is formed on or screwedto 'the-periphery" of the disk 35 and'exten'ds radially thereAV from. is indicated in Figures lll. and-12v the flange Ll() is composed'of a number of segments, each 'of which maybe in ithei formH of a portion of a helix; Against each of these segments opposed abutments such as set-screws'f 'bear-so Athat as the diskA is" rotated with respect to thedisk 36,l it is pushed toward or fromthe-latter, the rate of such motion at any moment beingde` tei-mined by the pitch ofthe' segments of the flange e0. In order to permitthe' as-' sembling of the gauge ofthe formv shown, the flange 3T of the disk 36 is preferably made separate therefrom and is secured" thereto kas by a suitable`v number: of Vscrews The lip 3801i the flange 37 neednot be continuous, but may be inthe' form of' radial Vprojections extending 'inwardly from l the flange, and of :suliicient size' to 'support a set-screw 39. By shapin'gvthe cam surfaces of thecanr fl() as desired,` the action of the gauge may be modified inthe same manneras the action ofthe gauges hereinbefore described.

In Figures 13, irland l5 is illustrated a gauge of the plug type embodying the pres entlnvention. As therein shown, this gauge may comprise a pair of external threads l5, 46, the thread 4 5 being mounted at the end of' a suitable spindle 47 having a knurled linger pieceY 4&8 secured at the further end. This spindle Yisrotatively fittedv within a sleeve 49, which carries the thread i6 atene end thereof. On its opposite end. a flange may be'provided, this flange having a lseries-ofslots 5l therethrough, the sides of which constitutev cam surfaces against which lmove cam followers such'asY pins 52, projecting from an enlarged portion 53 of the finger piece 4S, the portion 53 being preferably of disk form and fitted for rotation within the flange 50. On the end face of theflange I may provide suitable scale marks and/or Zone-indicating marks, as well as a mark to indicate the open position of the gauge wherein the threads 45 and 46 lie in a common helix. To cooperate with the marks on the flange 50 I may provide a suitable index 54 on the enlarged portion 53 of the finger piece 48. When the finger piece 48 is rotated relatively to the flange 50, the thread 45 also rotates relatively-to the thread 46. The slots 5l are preferably formed so as to cause bodily axial movement of the thread 45 relative to the thread 46 in such a manner as to modify the apparent relative axial movement of the threads caused by the rotation, as hereinbefore described in connection with the slots v26 and pins 27. In using a gauge of this type, the members are turned to the open position whereupon the gauge threads 45, 46 are screwed into engagement with a thread to be tested. The members are then relatively rotated in one direction, then the other, the amount of rotation possible in each case from the open position being observed. If the index 54 falls outside the zone of tolerance on either side, the tested piece may be rejected.

I claim:

1. A screw thread gauge comprising a pair of relatively rotatable members having gaging threads capable of lying in a common helix, and means connecting said members, said means including a cam of varying pitch and a cam follower for causing relative axial movement of said members when they are relatively rotated.

2. A screw thread gauge comprising a pair of relatively rotatable members having gaging threads capable of lying in a common helix and of receiving with a loose fit the maximum tolerable screw thread to be tested, and means connecting said gauge members and causing varying relative axial movement of said gauge members whenA relatively rotated, said means including a cam of varying pitch on one of said members and a cam follower on the other gauge member and in operative engagement with said cam.

3. A screw thread gauge comprising a pair of relatively rotatable disks having threaded bores the threads of which are capable of lying in a common helix and of a size to receive with a loose fit the maximum Vtolerable screw to be tested, means on said disks for holding said disks against relative radial movement, and means for causing controlled relative axial movement of said disks when relatively rotated, said latter means including a cam of varying pitch carried by one said disk and a cooperating cam follower carried by the other said disk.

4. A screw thread gauge comprising a pair of relatively rotatable disks having threaded bores the threads of which are capable of lying in a common helix and of a size to receive with a loose fit the maximum tolerable screw to be tested, means for holding said disks against relative radial movement, and means for causing controlled relative axial movement of said disks when relatively rotated, said latter means including a plurality of cams on one said disk jecting inwardly from said flange, each said cam follower being in cooperative engagement with one of said grooves.

6. A screw thread gauge comprising a pair of relatively rotatable disks having bores threaded to receive with a loose fit a screw to be tested having the maximum tolerable pitch diameter, a flange extending from the rim of one of said disks and forming a recess to receive the other said disk and cooperating elements on said fiange and other disk respectively for causing relative axial movement of the disks when relatively rotated, said cooperating elements including a cam slot and a cam follower projecting into said slot.

7. A screw thread gauge comprising a pair of relatively rotatable disks having threaded bores therethrough, the threads of which are capable of lying in a common helix and of receiving with a loose fit a screw to be tested having the maximum tolerable pitch diameter, a flange extending from the periphery of one of said disks and forming a recess to receive the other disk and to maintain the assembled disks coaxial, said other disk having a series of slots in the periphery thereof making a varying angle with the plane of the disk, and pins extending inwardly from said flange into said slots to cause relative axial movement of said disks when relatively rotated.

In testimony whereof I have affixed my signature.

l t JAMES HARTNESS. 

